Diagnostic tests: Bone mineral density: Testing for osteoporosis

Abstract

Bone mineral density: testing for osteoporosis SUMMARY Primary osteoporosis is related to bone loss from ageing.Secondary osteoporosis results from specific conditions that may be reversible.A thoracolumbar X-ray is useful in identifying vertebral fractures, and dual energy X-ray absorptiometry is the preferred method of calculating bone mineral density.The density of the total hip is the best predictor for a hip fracture, while the lumbar spine is the best site for monitoring the effect of treatment.The T-score is a comparison of the patient's bone density with healthy, young individuals of the same sex.A negative T-score of -2.5 or less at the femoral neck defines osteoporosis.The Z-score is a comparison with the bone density of people of the same age and sex as the patient.A negative Z-score of -2.5 or less should raise suspicion of a secondary cause of osteoporosis.Clinical risk calculators can be used to predict the 10-year probability of a hip or major osteoporotic fracture.A probability of more than 5% for the hip or more than 20% for any fracture is abnormal and treatment may be warranted.height (see Fig. ).The presence of a vertebral fracture is highly predictive of a subsequent fracture, but if the fracture is asymptomatic the patient may be left untreated and at risk.In a large Australian community-based study of women aged over 70 and not known to have osteoporosis, thoracolumbar X-ray detected at least one vertebral fracture in 24.7%.In the same cohort, dual energy X-ray absorptiometry found 21.8% had osteoporosis at the femoral neck or lumbar spine.However, only 7.3% had both osteoporosis on dual energy X-ray absorptiometry and a vertebral fracture on thoracolumbar X-ray. 2 Up to 50% of women with vertebral fractures have normal bone mineral density by dual energy X-ray absorptiometry, so potentially a third of women will not be diagnosed by this method.3 A thoracolumbar X-ray should therefore be performed in patients who have symptoms of a vertebral fracture, decreased bone mineral density on dual energy X-ray absorptiometry at the hip, or multiple clinical risk factors for osteoporosis.While spinal radiography is essential for diagnosing a vertebral fracture, it is important not to confuse the spinal deformity of an osteoporotic fracture from other causes including spondylosis.Another method for detecting vertebral fractures is through vertebral fracture assessment using dual energy X-ray absorptiometry.Multiple studies have